1. Field of the Invention
The present invention relates, generally, to bi-directional or xe2x80x9ctwo-wayxe2x80x9d clutch assemblies and, more specifically, to a two-way clutch assembly having selective actuation. In addition, the two-way clutch assembly of the present invention is particularly adapted for use in connection with a brake, clutch, or other holding device in a transmission to provide low and reverse gears.
2. Description of the Related Art
Generally speaking, land vehicles require three basic components. These components include a power plant (such as an internal combustion engine), a power train and wheels. The power train""s main component is typically referred to as the xe2x80x9ctransmission.xe2x80x9d Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. Transmissions include one or more gear sets, which may include an inner gear, intermediate planet or pinion gears that are supported by their carriers, and outer ring gears. Various components of the gear sets are held or powered to change the gear ratios in the transmission. In addition to such planetary gear sets, driveline components may further include multi-disc friction devices that are employed as clutches or brakes. The multi-disc pack clutch is a friction device that is commonly employed as a holding mechanism in a transmission, transfer case or differential or the like. In addition, multi-disc friction devices also find use in industrial applications, such as wet brakes, for example, to brake the wheels on earth-moving equipment.
The multi-disc pack clutch or brake assembly has a clutch sub-assembly including a set of plates and a set of friction discs that are interleaved between one another. The plates and friction discs are bathed in a continual flow of lubricant and in xe2x80x9copen packxe2x80x9d mode normally turn past one another without contact. The clutch or brake assembly also typically includes a piston. When a component of a gear set is to be held, as for example during a particular gear range, a piston is actuated so as to cause the plates and friction discs to come in contact with respect to one another. In certain applications, it is known to employ several multi-disc pack clutch devices in combination to establish different drive connections throughout the transmission, transfer case, or differential to provide various gear ratios in operation, or to brake a component.
When the discs are not engaged, there often remains a differential rotational speed between the drive and driven members that the clutch or brake bridges. Relative rotation between the friction discs and the plates during open-pack mode creates drag. This condition results in parasitic energy losses, reduces the efficiency of the transmission, transfer case or differential, and ultimately results in lower fuel efficiency.
In addition to multiple friction devices, one-way clutches are frequently employed in transmissions, transfer cases, and differentials to selectively transmit torque in one rotational direction, but not in the opposite rotational direction. To this end, one-way clutches typically include an inner race, an outer race, and an engagement mechanism disposed therebetween. The engagement mechanism is operable to lock the inner and outer races together thereby transmitting torque in one relative direction. The engagement mechanism is further operable to allow freewheeling rotation between the inner and outer races in the opposite rotational direction. Engagement mechanisms commonly used in one-way clutches of the related art include pawls, sprags, and rollers. A cage, along with biasing members, such as springs, are also sometimes employed to retain the pawls, sprags, or rollers between the inner and outer races as well as to selectively assist in the change of operational modes between torque translation and freewheeling actuation of the clutch, depending on the direction of rotation between the inner and outer races.
As noted above, one-way clutches of this type have been employed in numerous applications in transmission, transfer cases, and differentials. For example, one-way clutches have been employed in conjunction with friction clutches and planetary gear sets to effect low and reverse gear ratios in conventional transmissions. While this arrangement has worked well for its intended purpose, some disadvantages remain. For example, the friction clutch remains a source of significant parasitic losses due to inherent drag between the friction plates when the clutch is operating in xe2x80x9copen packxe2x80x9d mode. Specifically in the case of low and reverse gears, the associated friction clutch operates in open pack mode when the transmission is in gears 2-5 and therefore generated parasitic losses in each of these gears. Still, the clutch is necessary for providing the proper holding torque in low and reverse gears. Accordingly, there remains a need in the art for a mechanism that can provide the appropriate holding torque for both low and rear gears in the transmission and yet results in less parasitic losses than are presently attributable to the multiple plate friction clutch used for this purpose. In addition, there is a need in the art for a device that continues to perform the functions of the one-way clutch as described above, particularly where the output speed-of the transmission exceeds the input speed resulting in engine compression braking.
Partially in response to this problem, bi-directional or xe2x80x9ctwo-wayxe2x80x9d overrunning clutches have been proposed in the related art for use in these circumstances. These bi-directional overrunning clutch assemblies typically employ an inner race, an outer race, and a plurality of rollers, pawl, or sprags as the engagement mechanism disposed therebetween. Some of the bi-directional overrunning clutches of the type known in the related art are, for the most part, designed to be self-actuating. While they appear to present a solution to certain problems identified above, they have not been widely employed in transmission, transfer cases, and differentials of the related art. These self-actuating bi-directional overrunning clutches are relatively mechanically complex and have certain physical limitations and drawbacks. One such drawback is that the inner and outer races of the presently known bi-directional clutches generally travel over a large angular distance between the engagement in one rotational direction to the engagement in the opposite rotational direction. This makes for undesirable driving conditions by causing hard lockups when changing directions and also brings about a short mechanical life due to the severe inherent impact forces of the engagement. Additionally, the self-actuating bi-directional clutches known in the related art cannot be selectively engaged in an efficient manner or to optimize the vehicle power output in response to varying driving conditions.
In an attempt to overcome these problems, bi-directional overrunning clutches that may be selectively actuated to change the direction of torque translation and overrunning operation have been proposed in the related art. Unfortunately, these devices generally suffer from the disadvantage that they are mechanically complex, difficult to control and are generally not cost effective.
Accordingly, there remains a need in the art for a bi-directional clutch that can be selectively actuated and controlled in a manner to provide driving comfort and offer efficient operating modes for various driving conditions while at the same time facilitating the reduction in parasitic losses derived from conventional multi-disc friction devices. Furthermore, there remains a need in the art for a controllable bi-directional overrunning clutch assembly that can be quickly and easily shifted to provide either torque translation or freewheeling operation in either rotational direction. In addition, there also remains a need in the art for a bi-directional clutch assembly that can be effectively shifted between operational modes without jamming of the engagement mechanism or other failures occurring at the interface between the inner and outer races of the clutch assembly.
The present invention overcomes the disadvantages in the related art in a two-way clutch assembly that includes an inner race, and an outer race where the inner and outer races are supported for rotation about a common axis. An engagement mechanism is disposed between the inner and outer races. The engagement mechanism is operable to shift to a first position providing torque translation between the inner and outer races in one rotational direction while allowing relative freewheeling rotation between the inner and outer races in an opposite rotational direction. In addition, the engagement mechanism is operable to shift to a second position that provides torque translation and relative freewheeling rotation between the inner and outer races in rotational directions opposite to that provided by the engagement mechanism when disposed in the first position. Furthermore, an actuator assembly is operatively connected to the engagement mechanism. The actuator assembly acts to simultaneously move in an axial direction and rotate about the axis of rotation in an indexing manner in response to a biasing force to shift the engagement mechanism between the first and second positions to selectively provide torque translation and relative freewheeling rotation between the inner and outer races in either rotational direction.
In this way, the clutch assembly can be selectively shifted between operational modes without jamming of the engagement mechanism or other failures occurring at the interface between the inner and outer races of the clutch assembly. Thus, this type of clutch assembly may be employed as a component of an automotive driveline in a transmission, transfer case, or differential to eliminate other components while maintaining the requisite functionality even when transitioning among its various operational modes.
For example, the two-way clutch assembly of the present invention may be employed in conjunction with a friction clutch in a transmission that is used as a holding device. Together, the two-way clutch assembly and the friction device act in conjunction with a planetary gear set to provide low and reverse gears in a transmission. Another advantage of the clutch assembly of the present invention is that when the clutch is deployed with a low/reverse brake in connection with providing low and reverse gear ratios in a transmission, the brake may be closed at all times. In this way, the clutch assembly of the present invention reduces parasitic energy loss, improves operational efficiency, and reduces cost.